In a next generation, or 4th Generation (4G), communication system, research is being actively conducted to provide services having various Quality of Service (QoS) requirements, for example, a throughput of about 1 Gbps when stationary and a throughput of about 100 Mbps when on the move. In particular, research on the 4 G communication systems is ongoing so that mobility and QoS are ensured in a Broadband Wireless Access (BWA) communication system. Examples of the BWA system include a Wireless Local Area Network (WLAN) system and a Wireless Metropolitan Area Network (WMAN) system.
In order to improve transmission and reception throughput in the 4 G communication system, cooperative transmission using a relay station (RS) is considered. In the cooperative transmission, a transmitting end transmits a signal, and the signal is received by a receiving end and the RS. Thereafter, the RS retransmits to the receiving end the signal received from the transmitting end. As a result, the receiving end receives the signal from both the transmitting end and the RS. Therefore, a reception gain is obtained, and a high throughput can be achieved.
Throughput of the cooperative transmission can increase when an appropriate signal transmission policy is used between the transmitting end and the RS. One of methods for increasing the throughput of cooperative transmission is a method of determining a covariance matrix used for signal transmission of the transmitting end. That is, correlation between transmit (Tx) power of Tx antennas of the transmitting end and receive (Rx) power of Rx antennas of the receiving end and the RS is computed according to desired channel state information between nodes, and based on the computation result, Tx power for each antenna can be regulated when the transmitting end transmits a signal. Thus, the throughput of cooperative transmission can be improved. Furthermore, when the RS relays a signal, an optimal relay matrix may be determined to perform linear processing on the received signal, thereby improving the throughput of cooperative transmission.
As described above, communication quality can be improved by using the cooperative communication in the multi-antenna relay wireless communication system. In addition, the throughput of cooperative transmission can be improved by determining the covariance matrix for the transmitting end and the relay matrix for the RS. However, since there is no concrete method for optimizing the covariance matrix and the relay matrix, a problem arises when the cooperative transmission is performed.